Thermionic tube having a secondary-emission electrode



June 7, 1949. H. BIENFAIT ETAL 2,472,189

THERMIONIC TUBE HAVING A SECONDARY-EMISSION ELECTRODE Filed March 22, 1943 APPLY OXIDE OF NICKEL TUNGSTEN ZIRCONIUM OR MOLYBDENUM TO ELECTRODE SURFACE BEFORE PLACING IN TUBE REDUCE PART OF OXIDE AT LOW TEMPERATURE To FORM FINELY' DIVIDED BLACK METAL PARTICLES APPLY CAESIUM TO ELECTRODE SURFACE BY VAPORIZATION FIG. I

EMISSIVE MATERIAL HEAT RADIATING BLACK METAL PARTICLES CORNELIS FREDERIK VEENEMANS HENRI BIENFAIT INVENTORS ATTORNEY\ Patented June 7, 1949 THERMIONIC TUBE HAVING A SECONDARY- EIWISSION ELECTRODE Henri Bienfait and Cornelis Frederik Veenemans, Eindhoven, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford,

Conn., as trustee Application March 22, 1943, Serial No. 480,102 In the Netherlands July 3, 1941 Section 1, Public Law 690, August 8, 1946 Patent expires July 3, 1961 2 Claims.

This invention relates to thermionic tubes provided with a secondary-emission electrode and more particularly to such tubes in which the secondary emission is brought about by an active layer consisting of caesium oxide, which is applied to the secondary-emission electrode.

Thermionic tubes containing a secondaryemission electrode covered with caesium oxide as an active material are already known.

Further, it is already known to cool secondaryemission electrodes; to this end, it has been suggested either to connect cooling bodies to the secondary-emission electrodes, or to cool the latter with the aid of a running liquid.

Furthermore, in thermionic tubes it was already general practice to cover definite electrodes with a black substance in order to improve the radiation of heat and thus maintain the temperature of the electrode concerned at a low value. The black material used is frequently carbon.

In the accompanying drawing Figure 1 shows the steps of the method according to the invention and Figure 2 shows an enlarged cross-section of a portion of an electrode made in accordance with the invention.

In Figure 1 the rectangles represent the successive steps of the method of the invention. The finished electrode shown in Figure 2 comprises a base on which heat-radiating black metal particles are disposed and about which particles emissive material is deposited.

It has been found, however, that carbon is not adapted to be applied to parts of secondaryemission electrodes which contain caesium oxide as active material, since carbon very easily absorbs or adsorbs caesium. Since the active caesium coating is almost solely obtained by applying caesium to the secondary-emission electrode by vaporisation and subsequently oxidising, good dosing of the caesium is impossible if part of the electrode is covered with carbon. On the other hand, it is desirable that on the secondary-emission electrode or in the vicinity thereof there be a material capable of binding small quantities of caesium.

Also the cooling of the secondary-emission electrode is desirable, since the heating of the electrode produced during operation injuriously affects the emission. The temperature of the secondary-emission electrode during operation must in general not exceed C.

A thermionic tube according to the invention contains at least one secondary-emission electrode a part of whose surface contains caesium oxide as an active secondary-emission material, the other non-activated parts of the surface of the electrode or electrodes being covered with the product obtained by reduction of one or more of the oxides of nickel, tungsten, zirconium or molybdenum.

The reduction of these metal oxides has the effect of producing on the secondary-emission electrode a layer consisting of the metal having such structure as to exhibit a black appearance. This metal may still be mixed with a quantity of metal oxide, since the reduction is effected only partly.

According to a process which also forms part of the invention, a secondary-emission electrode is manufactured by applying, prior to its incorporation in the tube, to a part of the surface a layer consisting of one or more of the oxides of the metals nickel, tungsten, zirconium or molybdenum, and subsequently reducing this layer at low temperature.

The application of the metal oxides to the electrode may be efiected, for example, by spraying, dipping, or with the aid of the cataphoretic process.

The reduction at low temperature has the effect of producing a non-hardened, finely distributed structure of the metal which is particularly adapted to the emission of heat and the adherence of small quantities of caesium.

According to one particular example of a process according to the invention, the reduction is efiected during about 10 minutes at a temperature of about 700 C. The reduction may take place, for example, in a hydrogen atmosphere.

We claim:

1. A secondary-emissive electrode for a thermionic tube having a multiplicity of parts on its surface comprised of black particles of nickel,

and secondary-emissive material on the said electrode around said nickel particles.

2. The process of making a secondary-emission electrode for a thermionic tube which comprises depositing nickel oxide on the surface of said electrode, reducing said oxide to a metal in a. hydrogen atmosphere at a temperature of about 700 C., and depositing secondary emissive maumber terial around said metal particles. 2,123,024 HENRI IBIENFAIT. 2,146,099 CORNELIS FREDERIK VEENEMANS. 2, 2,190,695 REFERENCES CITED 2,198,329 2,204,252

The following references are of record in the m file of this patent:

UNITED STATES PATENTS Name Date Piore et a1 July 5, 1938 De Boer et a1 Feb. '7, 1939 Schreinemachers Aug. 29, 1939 Bruining et a1 Feb. 20, 1940 Bruining et a1 Apr. 23, 1940 Krenzlen June 11, 1940 

